In the U.S., Latinas report high rates of inactivity and related conditions (obesity, diabetes). Effective interventions that leverage state-of-the-art theory and methods are needed to address such health disparities. We recently conducted a randomized controlled trial of a culturally/linguistically adapted, print-based, mail- delivered physical activity (PA) intervention for Latinas (Seamos Saludables, R01 NR011295), in which participants (N=266) received either individually tailored PA intervention materials based on the Transtheoretical Model and Social Cognitive Theory, or printed wellness materials. Changes in moderate to vigorous PA (MVPA) were significantly greater in the intervention arm from baseline to six months (1.87 min/week to 73.37 min/week) than the control arm (3.02 min/week to 32.98 min/week). These increases were maintained at 12 months and mediated by changes in psychosocial constructs targeted by the intervention. A renewal of R01NR011295 is proposed to replicate these findings in Mexican Americans (who comprised only 5% of the original sample but most of US Latino population), explore its clinical potential in preventing and managing chronic disease, and to improve the intervention's effectiveness by incorporating participant feedback (desire for increased interactivity and accountability), further targeting SCT constructs that were overall not influenced by the original intervention yet improved amongst the most successful participants (social support and outcome expectancies), and responding to changing trends and technology use in the Latino population (adding text messaging). In the proposed study, 250 Mexican American women will be randomized to either 1) the original, empirically supported Seamos Saludables tailored print intervention or 2) the technology and theory-enhanced version of the Seamos Saludables intervention. Data will be collected at baseline, 6 months (post-treatment), and 12 months (maintenance) using well-established objective (accelerometers) and subjective (7 Day PAR) PA measures, as well as a comprehensive set of psychosocial questionnaires. We hypothesize that at the end of treatment (month six) the Enhanced Tailored Intervention participants will report significantly more minutes/week of MVPA than the Original Tailored Intervention participants. We will also examine changes in cardiovascular and metabolic biomarkers (fasting blood glucose, HbA1c, triglycerides, LDL, HDL, HS-CRP), maintenance of treatment effects at 12 months, costs of delivering the enhanced vs. original intervention programs, potential mediators and moderators of the intervention- physical activity relationship, and will also compare the efficacy of the original Seamos Saludables program in Mexican American women to results in the original population (who were mostly Dominican, Colombian, and Puerto Rican). Such high-reach, low-cost strategies for promoting physical activity have great potential for adoption on a larger scale and could have a large impact on reducing health disparities.